Tobacco smoke essentially consists of a dispersion of solid and liquid particles in air, and this dispersion will be referred to as an aerosol in this specification. The aerosol is extremely stable due to the small size of the particles concerned and hence gravity has a negligible effect compared with the effect of convection currents and Brownian movement. Tobacco smoke is thought to contain constituents injurious to health and many suggestions have been made of filters to at least partially remove constituents of the smoke prior to entry into the smoker's mouth.
Tar and nicotine values of tobacco smoke entering the smoker's mouth, i.e., after filtration, are considered by Government bodies to be a significant indication of the effectiveness of a filter to remove injurious components of tobacco smoke. While it is possible by filtration to achieve very low levels of tar and nicotine values in tobacco smoke, frequently this is at the expense of taste and smoker satisfaction. For example, the filter may not allow adequate quantities of smoke to pass through the filter owing to the filter density required to achieve the low tar and nicotine level and hence the "draw" of the cigarette may not be satisfactory to the consumer.
Tobacco smoke filters of polyolefin have been suggested heretofore in U.S. Pat. No. 2,966,157. However, the fibers forming this prior art filter medium have diameters considerably in excess of 5 microns and are crimped.
Crimping of the filamentary material for tobacco smoke filters usually is considered necessary in order to displace portions of the individual filaments at angles to the axis of the filter tow so that, in the filter, these displaced portions of the filaments will be disposed across the flow path of the tobacco smoke for intercepting the particles to be filtered from the smoke. The crimping and crimp-deregistering operations are particularly critical to the production of high quality filters from cellulose acetate filaments and have been thought to be necessary for polyolefin fibers, as described in U.S. Pat. No. 2,966,157 referred to above. However, such operations add materially to the cost of production, and unless they are carried out with care, products lacking in uniformity are apt to result. It has been found that the fibers used in the filters of the present invention do not require the crimping of the individual fibers to provide effectiveness.